# Comparison of compression

April 4, 2011
By

(This article was first published on binfalse » R, and kindly contributed to R-bloggers)

I recently wrote an email with an attached LZMA archive. It was immediately answered with something like:

What are you doing? I had to boot linux to open the file!

First of all I don’t care whether user of proprietary systems are able to read open formats, but this answer made me curious to know about the differences between some compression mechanisms regarding compression ratio and time. So I had to test it!

This is nothing scientific! I just took standard parameters, you might optimize each method on its own to save more space or time. Just have a look at the parameter -1..-9 of zip. But all in all this might give you a feeling for the methods.

# Candidates

I’ve chosen some usual compression methods, here is a short digest (more or less copy&paste from the man pages):

gzip
uses Lempel-Ziv coding (LZ77), cmd: tar czf $1.pack.tar.gz$1
bzip2
uses the Burrows-Wheeler block sorting text compression algorithm and Huffman coding, cmd: tar cjf $1.pack.tar.bz2$1
zip
analogous to a combination of the Unix commands tar(1) and compress(1) and is compatible with PKZIP (Phil Katz’s ZIP for MSDOS systems), cmd: zip -r $1.pack.zip$1
rar
proprietary archive file format, cmd: rar a  $1.pack.rar$1
lha
based on Lempel-Ziv-Storer-Szymanski-Algorithm (LZSS) and Huffman coding, cmd: lha a $1.pack.lha$1
lzma
Lempel-Ziv-Markov chain algorithm, cmd: tar --lzma -cf $1.pack.tar.lzma$1
lzop
imilar to gzip but favors speed over compression ratio, cmd: tar --lzop -cf $1.pack.tar.lzop$1

All times are user times, measured by the unix time command. To visualize the results I plotted them using R, compression efficiency at X vs. time at Y. The best results are of course located near to the origin.

# Data

To test the different algorithms I collected different types of data, so one might choose a method depending on the file types.

## Binaries

The first category is called binaries. A collection of files in human-not-readable format. I copied all files from /bin and /usr/bin, created a gpg encrypted file of a big document and added a copy of grml64-small_2010.12.iso. All in all 176.753.125 Bytes.

Method Compressed Size % of original Time in s
gzip 161.999.804 91.65 10.18
bzip2 161.634.685 91.45 71.76
zip 179.273.428 101.43 13.51
rar 175.085.411 99.06 156.46
lha 180.357.628 102.04 35.82
lzma 157.031.052 88.84 129.22
lzop 165.533.609 93.65 4.16

Binary

## Media

This is a bunch of media files. Some audio data like the I have a dream-speech of Martin-Luther King and some music. Also video files like the The Free Software Song and Clinton’s I did not have sexual relations with that woman are integrated. I attached importance to different formats, so here are audio files of the type ogg, mp3 mid, ram, smil and wav, and video files like avi, ogv and mp4. Altogether 95.393.277 Bytes.

Method Compressed Size % of original Time in s
gzip 88.454.002 92.73 6.04
bzip2 87.855.906 92.10 37.82
zip 88.453.926 92.73 6.17
rar 87.917.406 92.16 70.69
lha 88.885.325 93.18 14.22
lzma 87.564.032 91.79 74.76
lzop 90.691.764 95.07 2.28

Media

## Office

The next category is office. Here are some PDF from different journals and office files from LibreOffice and Microsoft’s Office (special thanks to @chschmelzer for providing MS files). The complete size of these files is 10.168.755 Bytes.

Method Compressed Size % of original Time in s
gzip 8.091.876 79.58 0.55
bzip2 8.175.629 80.40 8.58
zip 8.092.682 79.58 0.54
rar 7.880.715 77.50 3.72
lha 8.236.422 81.00 3.29
lzma 7.802.416 76.73 5.62
lzop 8.358.343 82.20 0.21

Office

## Pictures

To test the compression of pictures I downloaded 10 files of each format bmp, eps, gif, jpg, png, svg and tif. That are the first ones I found with google’s image search engine. In total 29’417’414 Bytes.

Method Compressed Size % of original Time in s
gzip 20.685.809 70.32 1.65
bzip2 18.523.091 62.97 10.71
zip 20.668.602 70.26 1.72
rar 18.052.688 61.37 8.58
lha 20.927.949 71.14 5.97
lzma 18.310.032 62.24 21.09
lzop 23.489.611 79.85 0.57

Pictures

## Plain

This is the main category. As you know, ASCII content is not saved really space efficient. Here the tools can riot! I downloaded some books from Project Gutenberg, for example Jules Verne’s Around the World in 80 Days and Homer’s The Odyssey, source code of moon-buggy and OpenLDAP, and copied all text files from /var/log. Altogether 40.040.854 Bytes.

Method Compressed Size % of original Time in s
gzip 11.363.931 28.38 1.88
bzip2 9.615.929 24.02 13.63
zip 12.986.153 32.43 1.6
rar 11.942.201 29.83 8.68
lha 13.067.746 32.64 8.86
lzma 8.562.968 21.39 30.21
lzop 15.384.624 38.42 0.38

Plain

## Rand

This category is just to test random generators. Compressing random content shouldn’t decrease the size of the files. Here I used two files from random.org and dumped some bytes from /dev/urandom. 4.198.400 Bytes.

Method Compressed Size % of original Time in s
gzip 4.195.646 99.93 0.23
bzip2 4.213.356 100.36 1.83
zip 4.195.758 99.94 0.2
rar 4.205.389 100.17 1.65
lha 4.194.566 99.91 2.04
lzma 4.197.256 99.97 1.98
lzop 4.197.134 99.97 0.1

Rand

## Everything

All files of the previous catergories compressed together. Since the categories aren’t of same size it is of course not really fair. Nevertheless it might be interesting. All files together require 355.971.825 Bytes.

Method Compressed Size % of original Time in s
gzip 294.793.255 82.81 20.43
bzip2 290.093.007 81.49 141.89
zip 313.670.439 88.12 23.78
rar 305.083.648 85.70 246.63
lha 315.669.631 88.68 64.81
lzma 283.475.568 79.63 258.05
lzop 307.644.076 86.42 7.89

Complete

# Conclusion

As you can see, the violet lzma-dot is always located at the left side, meaning very good compression. But unfortunately it’s also always at the top, so it’s very slow. But if you want to compress files to send it via mail you won’t bother about longer compression times, the file size might be the crucial factor.
At the other hand black, green and grey (gzip, zip and lzop) are often found at the bottom of the plots, so they are faster but don’t decrease the size that effectively.

All in all you have to choose the method on your own. Also think about compatibility, not everybody is able to unpack lzma or lzop..
My upshot is to use lzma if I want to transfer data through networks and for attachments to advanced people, and to use gzip for everything else like backups of configs or mails to windows user.

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